The invention resides in a method for in situ cleanup of soil contaminated by pollutants wherein the pollutants are extracted from the soil by a micro-emulsion containing oil compounds and further in a micro-emulsion containing oil compounds that are suitable for the method.
Micro-emulsions are thermodynamically stable, optically isotropic dispersions of two or more immiscible liquids, liquid mixtures or solutions which are stabilized by adding at least a third amphiphilic component.
Most natural and technical micro-emulsions are comprised of water and oil or fat as immiscible phases. Such micro-emulsions can be stabilized by molecules having hydrophilic as well as lipophilic properties, for example, by surfactants. Depending on the composition and ratio of the phases there are three possibilities of distribution. If water is the outer and oil is the inner phase, an O/W micro-emulsion is present whose basic character is determined by the water. If oil is the outer and water the inner phase, a W/O micro-emulsion is present whose basic character is determined by the oil. In bi-continuous micro-emulsions the two immiscible liquids are not present as discrete droplets but are continuously distributed.
A wide range of technical applications is known for micro-emulsions, including their use as solvents for chemical reactions, as formulations in the medical, pharmaceutical, and cosmetics fields, and as extraction agents, for example, for removing pollutants from soils.
For the in situ cleanup of contaminated soils according to known methods, solutions containing surfactants are used (see, for example, Visser, J. et al.: Surfactants in the Mobilization of Pollutants, in: Contaminated Soil &gt;95, Vol. II, eds.: van den Brink, W. J. et al., Kluwer Academic Publishers, Dordrecht, 1995, 1373-1374; Rosenstock, F. et al.: Process of Treating Contaminated Soils, U.S. Pat. No. 5,223,147; Schafer, G. et al.: Reinigung eines mit Dieselol kontaminierten kunstlichen Aquifers unter Einsatz von Tensiden, in: In-situ Technologie zur Grundwasser- und Altlasternsanierung, Kurzfassung zum VEGAS Workshop & BMBF/PWAB-Seminar, eds.: Institut fur Wasserbau der Universitat Stuttgart, Stuttgart, 1996, 19-20). For the elimination of pollutants that are nearly insoluble in water, such as polycyclic aromatic hydrocarbons, the use of oil-in-water micro-emulsions with very low oil contents (&lt;1%) has been suggested (see, for example, Bonkhoff, K et al.: Extraktion von polyzyklischen aromatischen Kohlenwasserstoffen aus belasteten Boden, in: Fremdstoffe in Boden Akkumulation, Bioverfugbarkeit, Bewertungsansatze, eds.: Arbeitsgemeinschaft der Gro.beta.forschungseinrichtungen AGF, Bonn 1994, 34-36; Bonkhoff K. et al.: Extraktion von PAK aus belasteten Boden, in: Erdol & Kohle Erdgas Petrochemie 1995, 48 (2) 63-64; Bonkhoff et al.: Basic investigations for an in situ-soil remediation with O/W micro-emulsion, in: Contaminated Soil &gt;95, Vol. II, eds.: van den Brink, W. J. et al., Kluwer Academic Publishers, Dcrdrecht 1995, 957-967; Bonkhoff, K. et al. Bodensanierung mit Mikroemulsion --von der Extraktion bis zu mikrobiellen Nachsorge, in: Schriftenreihe Biologische Abwasserreinigung, eds.: SFB 193; Biologische Behandlung industrieller und gewerblicher Abwasser, Technische Universitat Berlin, Berlin 1996). Furthermore, a cleanup method is known from published international patent application WO 94/04289 and also from U.S. Pat. No. 5,833,756 according to which the organic pollutants are extracted from the fine grains of solids by means of a micro-emulsion.
The use of micro-emulsions for all of the aforementioned applications has the disadvantage that, at low temperatures, the stability of the micro-emulsion is often impaired. At temperatures of .quadrature.20.quadrature. C. a micro-emulsion forms liquid crystals and is then no longer suitable for the aforementioned applications.
It is therefore an object of the present invention to provide a method for in situ cleanup of soils in which the pollutants are extracted from the soil by a micro-emulsion without the micro-emulsion forming liquid crystals so that the micro-emulsion can be used at temperatures of 0.degree. C. to 20.quadrature..degree. C. It is further an object of the present invention to provide suitable micro-emulsions for the method.